1. Technical Field
This invention relates generally to a locking device for locking one end of a rod to an end of an element to prevent inadvertent separation and, specifically, to such a device for use in the airline industry.
2. Description of Related Art
Most military and commercial aircraft utilize combinations of bellcranks, push/pull rods, bungees (spring loaded pushrods) and hydraulic actuators to operate flight controls and landing gear systems. Since bungees and hydraulic actuators have a tendency to produce relative rotary motion during operation, system integrity has frequently depended upon anti-rotation locking devices to prevent such motion. Those skilled in the art strive to meet the specifications of military and government regulations for airline safety. The specifications and regulations that govern the design and construction of aircraft systems include MIL-F-9490 General Specification for Flight Control System Design Installation and Test of Piloted Aircraft (U.S. Air Force), General Specification for Design and Construction of Aircraft Weapon Systems SD24L (U.S. Navy), Military Specifications MIL-F-18372 Flight Control Systems: Design, Installation and Test of Aircraft, and the Code of Federal Regulations 14, Aeronautics and Space. The invention is in strict compliance with the above-noted specifications and regulations, whereas existing standard rod end locking devices may not be in strict compliance.
These standards attempted to preclude human error of installation by providing tabs, slots, and grooves to integrate the locking devices. However, the installation of components such as those described above can be forced, with the assembly of the elements being incorrect regardless of the efforts made to ensure correct installations. It has been reported that over one-third of aircraft inspected for standards compliance contained improperly assembled components, and over one-fourth of these were critical linkages. A disconnect of only one component can cause a loss of linkage from pilot to control members. The consequence of such a failure could result in uncontrollable flight or an uncontrollable landing, and possibly the subsequent loss of an airplane.
For example, existing locking devices are highly dependent upon safety wire that is designed to prevent a jam nut from backing off. If the jam nut backs off, the locking device may eventually disconnect due to vibration. It is possible for a technician to improperly install standard rod-end locking devices backwards, neglect to tighten any jam nuts with sufficient torque, or inadvertently omit safety wiring. Additionally, the components may be incorrectly assembled with tabs and slots being misaligned. Moreover, any exposure of the locking device to lubricants, such as oil or grease, can reduce the friction between the piston rod and any jam nuts, thereby accelerating the loosening of those components. Any of these mistakes could result in a catastrophic failure because failure of a locking device can lead to a total failure of a particular control system. Loss of a control system can render a pilot helpless and leave the aircraft uncontrollable.
U.S. Pat. No. 5,362,110 issued on Nov. 8, 1994 to Bynum discloses a capture device that prevents vibrational disassembly of fluid tubing couplers and fasteners for hydraulic, pneumatic, and fuel systems on aircraft. Two components of a coupling are held together when a capture device on one component engages a shoulder on the second component. The capture device and the shoulder act to prevent axial separation of the two components. However, rather than latch and spring components, the capture device consists of tangs which depend on the stiffness of the tang material to lock onto the other component. In addition, the purpose of the tangs is not preventing axial separation but preventing relative rotation by creating a ratcheting effect with the second component. Furthermore, no mechanisms operate independently of the tangs in case the tangs fail or are not properly engaged. Also, only the torque from a wrench is necessary to disengage the capture device. For example, spring locks do not need to be compressed to unlock the components.
U.S. Pat. No. 4,684,284 issued on Aug. 4, 1987 to Bradley, Jr., discloses an anti-rotation lock assembly that uses wedge keys in combination with a jam nut. However, the patent does not disclose the use of a nut with a special locking thread form or other mechanism to resist backing off.
U.S. Pat. No. 4,232,978 issued on Nov. 11, 1980 to Cohen discloses a double locking device for securing actuator rods to rod-ends which precludes the possibility of disengagement by providing a double locking feature with safety wiring. However, the use of the double locking device requires significant modification to the existing components to be locked, and thus, is undesirable for many applications.
Similarly, U.S. Pat. No. 4,274,754 issued on Jun. 23, 1981 to Cohen discloses a double locking device with a jam nut feature that precludes the possibility of reverse assembly. However, since the device of the '754 patent uses the same core locking device as the '978 patent, the use of the double locking device also requires significant modification to the existing components to be locked, and thus, is undesirable for many applications.